Mix sauce ingredients (mayonnaise, sour cream, tajin, lime juice, and milk) in a bowl and set aside.

Season chicken breasts on both sides with salt, pepper, chili powder, cumin, paprika, garlic powder, and oregano. Heat a skillet over medium heat, add olive oil, and cook chicken until cooked through (165 degrees), flipping once. Remove to a plate.

In the same skillet, add more oil if needed, then add corn, onion, and jalapeno. Turn heat to high, cover, and saut? until corn is charred and tender, about 4-5 minutes. Remove from heat and stir in half of the sauce.

To assemble, spoon rice into a bowl, top with chicken, street corn, avocado, cotija cheese, and cilantro. Serve with lime wedges and extra sauce if desired.