For the enchilada sauce: In a small saucepan over medium heat, add oil and flour. Stir in tomato paste, cumin, oregano, chili powder, salt, and pepper. Add water and bring sauce to a simmer. Cook for 10-15 minutes until sauce thickens, stirring occasionally. Remove from heat.
Combine 1 cup cooked rice, lime juice and 1 tbsp cilantro in a bowl and set aside.
In a large skillet over medium heat, add 1 tbsp olive oil and diced onion. Cook for 8-10 minutes until onions are soft. Add shredded rotisserie chicken, salt, pepper, chili powder, oregano, cumin, garlic powder and stir to combine. Remove from heat.
Preheat oven to 375 degrees.
Pour about half of the enchilada sauce in the bottom of a large baking dish (about 9" x 13"). Assemble the burritos; Evenly distribute black beans, white rice, chicken mixture and cheddar cheese between all four burritos. Fold the burritos and transfer them to the baking dish with the enchilada sauce. Pour remaining enchilada sauce on top of the burritos.
Cover the dish is foil and bake for 25 minutes.
Remove burritos from the oven. Top with sour cream, cilantro and sliced avocado. Enjoy!