Preheat oven to 350.
Grease a 13x9-inch baking dish with cooking spray and set aside.
Heat olive oil over medium-heat in a large skillet.
Add onions and cook for 3 minutes.
Stir in garlic and continue to cook for 1 minute.
Add chicken, 2/3 of the diced tomatoes, and sour cream; season with oregano, basil, salt and pepper, and chili powder.
Cook for 5 minutes, or until heated through.
Mix in 1/2 of the shredded cheddar cheese.
Spoon mixture down the center of each tortilla and roll up.
Place seam side down in prepared baking dish.
Bake for 10 minutes.
Top with the rest of the diced tomatoes and shredded cheese.
Return to oven and bake for 5 to 10 minutes, or until cheese is melted.