Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease the cups.
In a large bowl, whisk together 2 cups flour, granulated sugar, baking powder, baking soda, and salt until well combined.
In a separate medium bowl, whisk together melted butter, Greek yogurt, eggs, milk, lemon zest, lemon juice, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently fold together with a spatula until just combined. Do not overmix; some lumps are okay.
In a small bowl, prepare the streusel topping by combining brown sugar, 1/2 cup flour, and ground cinnamon. Add cold cubed butter and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
Divide the muffin batter evenly among the 12 muffin cups, filling each about 3/4 full.
Sprinkle the streusel topping evenly over each muffin.
Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.