Preheat oven to 350. Spray a large skillet with nonstick cooking spray, and heat over medium-high heat. Add onion and bell pepper to skillet;cook,stirring frequently,for 5 minutes or until onion starts to soften. Add cream cheese and soup; reduce heat to low, and stir until cream cheese melts.Remove from heat.
Add chicken, 1 1/2 cups cheddar cheese, tomatoes, oregano, cumin,and chili powderto cream cheese mixture, stiring until well combined.
Spoon into a 9-inch square baking dish. Sprinkle remaing 1/2 cup cheese over dip. Bake, uncovered, for 10 minutes or until bubbly.