Start by thoroughly squeezing the spinach dry using a clean kitchen towel or paper towels—this is crucial to prevent soggy burritos. Mince the garlic cloves and have all ingredients measured and ready. Shred or cut the chicken into 1/2-inch pieces if not already done. Combine the 2 cups cheddar cheese, 1/2 cup parmesan cheese, cumin, and lime juice in a bowl and set aside.

In a large pot or skillet, combine the shredded chicken, squeezed spinach, minced garlic, sour cream, and salsa over medium heat. Stir constantly as the mixture heats through, about 5 minutes. Pour in the lightly beaten eggs and continue stirring until they're fully cooked and incorporated into the filling, another 2-3 minutes. Add the cheese mixture from Step 1 and stir until all the cheese melts completely and the filling is cohesive. I like to let the filling cool for a few minutes before filling the tortillas—it makes them much easier to roll without the filling sliding out.

While the filling cools slightly, preheat your oven to 325°F. Lightly grease a 9x13 inch baking dish or similar sized casserole dish with cooking spray or oil.

Lay out a tortilla on a clean surface and place about 1/3 cup of the cooled filling from Step 2 in the center, leaving space on the sides. Fold in the left and right edges about 2 inches, then roll tightly from the bottom up, keeping tension as you go to create a snug burrito. Place seam-side down in the prepared baking dish and repeat with the remaining tortillas and filling. Once all 8 burritos are arranged in the dish, sprinkle the 1 1/4 cups cheddar cheese evenly over the tops.

Bake the burritos in the preheated 325°F oven for 20-30 minutes, until the cheese on top is melted and starting to bubble slightly. Remove from the oven and let rest for 5 minutes. Top each burrito with a dollop of the 1/2 cup sour cream and scatter the diced tomatoes over the top for freshness and color.