Heat 1 tbsp olive oil in a large pot over medium heat. Add 1/2 medium diced onion and 3 cloves minced garlic and sauté until the onion is translucent, about 8–10 minutes, stirring regularly.
Add 1 tsp chili powder, 1/2 tsp ground cumin, 1/2 tsp dried oregano, 1 tbsp brown sugar and 1/2 tsp salt to the pot and cook for 30 seconds on medium-low to bloom the spices.
Stir in 28 oz tomato sauce and 1.5 cups chicken stock. Bring to a simmer, cover, and cook on medium-low for 15–20 minutes. Cool slightly and blend until smooth if desired.
While the sauce simmers, heat a large skillet over medium-high and add 1/2 tbsp olive oil. Add the sliced red onion and orange pepper and 1/2 tbsp salt, and sauté for about 5 minutes, stirring.
Add 1 tbsp butter (or olive oil) to the skillet and continue cooking another 5–10 minutes, stirring occasionally, until the vegetables are cooked to your liking. Remove from heat.
In a large bowl, combine 2 cups cooked diced chicken, 1/2 cup corn kernels, the sautéed onions and peppers, and 3/4 cup shredded cheddar (half of the 1.5 cups).
Lay one large tortilla flat and place about 1/4 of the filling in a line down the center, leaving about 2 inches at each end. Fold the sides in and roll tightly with the seam down. Repeat for remaining tortillas.
Preheat the oven to 375°F. Spread half of the 3 cups enchilada sauce across the bottom of a deep oven-safe baking dish.
Place the rolled enchiladas seam-side down in the dish. Pour the remaining enchilada sauce over the top to fully cover, drizzle a little olive oil if desired, and sprinkle with the remaining 3/4 cup cheddar cheese.
Bake at 375°F for 15–20 minutes, until the cheese is melted and bubbly. Let rest briefly, then garnish with chopped cilantro and serve with desired sides.
Alternate smoking method: preheat pellet smoker to 350°F, assemble enchiladas in a deep pan with sauce and cheese as above, and smoke for 30–45 minutes until cheese is melted and bubbly.
Alternate air-fryer method: preheat air fryer to 375°F for 5 minutes. Place enchiladas on parchment brushed with a little olive oil, top with sauce and cheese, and air fry 5–10 minutes until cheese is melted.