In a large mixing bowl, stir together the chopped chicken, onion, green pepper, soups, Ro-Tel, chili powder, garlic, and cheese.
Slice the corn tortillas into approximately 1" pieces with a pizza cutter (or just tear them).
Lightly spray your slow cooker with non-stick spray, or use a liner.
Layer one third of the tortilla pieces into the bottom of the slow cooker. Top with one third of the chicken mixture. Repeat layers twice. Top with additional cheese, if desired.
Cover and cook on LOW for 3.5 hours.
After 3.5 hours, remove the lid and cook an additional 30 minutes for oven baked flavor and texture.