Preheat oven to 400˚F.
Heat oil in a large skillet over medium-high heat.
Add onions and cook for 2 minutes, stirring frequently.
Stir in garlic and cook for 30 seconds, or until fragrant.
Add chicken and season with salt, pepper, chili powder, cumin, and oregano; mix around until well combined.
Stir in Enchilada sauce - you can use more sauce if you like, or if it looks too dry - and continue to cook for 3 minutes.
Remove from heat.
Add about 1/4 cup Enchilada sauce to the bottom of a 9x13 baking dish.
Fill 8 flour tortillas with the chicken mixture; roll them up and transfer to the baking dish, seam-side down.
Lightly spray Enchiladas with Cooking Spray.
Top Enchiladas with remaining Enchilada Sauce and sprinkle with cheese.
Cover with foil and bake for 20 minutes.
Remove foil and continue to bake for 3 to 4 more minutes, or until cheese is completely melted and top is a light golden brown.
Remove from oven.
Top with sour cream, avocado slices, halved cherry tomatoes, jalapeno slices, and chopped cilantro.
Serve with lime wedges.