Preheat oven to 350 F.
Heat olive oil (2 tablespoons) over medium heat in a large pan (I like to use a 9" oven-safe skillet so I use only one pan for the entire recipe!). Once shimmering, add red bell pepper (1 chopped), red onion (1 chopped), salt (2 teaspoons), and pepper (1 teaspoon). Saute until softened.
Add the chili powder (1 tablespoon), cumin (1 tablespoon), and dried oregano (2 teaspoons), and toast until fragrant - about 2 minutes.
Remove pan from heat, and add sour cream (1/2 cup), salsa (1 cup), and 1 Lb cooked/shredded chicken breast (1 Lb). Stir to combine.
If you aren't using an oven-safe pan, transfer ingredients to an 8x8 casserole dish.
Pour heavy cream (1/4 cup) evenly over the top and sprinkle with shredded cheese (1 cup).
Bake in preheated oven for 30 minutes, or until casserole is warmed all the way through and the cheese has lightly browned. Top with cilantro and enjoy!