Whisk the warm water, sugar, and yeast together in a large bowl, then leave undisturbed for 10 minutes. A foamy layer indicates activity; an unchanged surface may mean the yeast is expired.

Stir the olive oil into the activated mixture. The oil will disperse through the liquid.

Work in the flour, salt, and cinnamon with a wooden spoon or silicone spatula for about 1 minute. Expect a loose, sticky mass rather than a smooth bread ball.

Place plastic wrap or a kitchen towel over the bowl and rest the dough for 30 minutes. The dough should remain soft and moist beneath the cover.

Reach beneath one side of the dough, lift it gently without tearing, and lay it across the center; turn the bowl 90 degrees and repeat until all four sides have been folded. These four directional folds make up the first folding set.

Cover the bowl again and allow a 30-minute rest. The folded dough will relax back into the bowl.

Complete a second set of four directional folds, then cover and rest for 30 minutes. Lift gently enough to preserve the dough's developing elasticity.

Repeat the four-direction folding set a third time, followed by another covered 30-minute rest. The dough should begin to feel more cohesive while remaining sticky.

Perform the fourth folding set, cover the bowl, and let the dough rise for 1 hour. Look for roughly doubled volume and bubbles across the surface.

Heat the blueberries, sugar, lemon zest, lemon juice, and vanilla in a small saucepan over medium heat, maintaining a simmer for 10 minutes. The berries should soften and release their juices.

Stir in the cornstarch, keep the mixture boiling for 1 minute while stirring continuously, then set it aside to cool. The filling should thicken rather than remain watery.

Distribute 3 tablespoons of melted butter across the interior of a 9x13-inch baking dish. The dish should have a generous buttery coating.

Cover the dish containing the dough with plastic wrap and allow a room-temperature rise of 1 hour. The dough is ready when it looks inflated and gently jiggles as you move the dish.

Use a fork or spoon to combine the topping's flour, sugar, lemon zest, and melted butter in a small bowl, then set aside. The mixture should form loose crumbs.

Heat the oven to 450°F (230°C). The oven should reach the set temperature before the dough goes in.

Spread the remaining 3 tablespoons of melted butter over the dough, distribute the cooled blueberry filling, and scatter the streusel across it. Aim for an even spread of fruit and crumbs rather than concentrated piles.

Coat your fingers generously with olive oil or butter left in the melting bowl, then press through the dough to the bottom of the dish, pushing berries into the indentations. Well-greased fingertips should release cleanly instead of pulling and tearing the dough.

Bake for 20-22 minutes, then leave the focaccia to cool for at least 30 minutes before cutting. Both the bread and streusel should look golden brown when baking is complete.