Preheat your oven to 350°F. This will ensure it's ready for baking your enchiladas to melty perfection.
Cook the onion and jalapeño in oil over medium heat until softened, about 5 minutes. Add the chili powder, garlic, brown sugar, cumin, oregano, and salt, cooking for another minute until fragrant.
Pour in the tomato sauce and stock, bringing the mixture to a simmer. Let it cook for 5 minutes, then remove from heat.
In a separate pan, cook the chicken breasts until no longer pink inside, about 20 minutes. Let them cool, then shred the meat with two forks.
Mix the shredded chicken with half of the cheese, cilantro, and the juice of the lime. This will be your enchilada filling.
Dip each tortilla in the sauce to lightly coat, fill with the chicken mixture, roll up, and place seam-side down in a baking dish.
After all tortillas are filled and placed in the dish, pour the remaining sauce over the top and sprinkle with the remaining cheese.
Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and slightly golden.
Let the enchiladas cool for a few minutes before serving. Garnish with extra cilantro if desired.