Heat 1 tablespoon of oil in a nonstick pan over medium-high heat. Add onion, tomato paste, garlic, oregano, red pepper flakes, 1/4 teaspoon salt. and 1/4 teaspoon pepper. Cook until onions are softened and tomato paste is rust in color, about 4 minutes.
Transfer onion-tomato paste mixture to a lightly greased crock pot (or use a crock pot liner) and stir in drained diced tomatoes.
Dissolve the cornstarch in the 1 tablespoon of water and stir into the tomato sauce.
Season chicken with salt and pepper and lay them on top of tomato mixture so that they are shingled and the tapered ends face the side of the crock pot with the control panel. Cover and cook on LOW for 3 to 4 hours.
Mix together mozzarella and half of the Parmesan cheese. Sprinkle cheese mixture over chicken, place the lid back on and let sit in turned-off crock pot for 15 minutes to melt the cheese.
Combine Panko crumbs and 1 tablespoon olive oil in a nonstick pan over medium heat. Cook until nicely browned, stirring frequently. Transfer Panko crumbs to a bowl to cool and then add in remaining Parmesan cheese, the basil, 1/8 teaspoon salt, and 1/8 teaspoon pepper. Sprinkle on top of cheese and serve.