Heat the oil in a large skillet or sauté pan over medium heat. Add the sausage and onion; cook for 5 minutes or until lightly browned. Turn the heat to low. Pour the eggs into the skillet. Cook slowly, constantly stirring with a wooden spoon until the eggs are firm but still moist. Remove from the heat, season with salt and pepper, and stir in the cilantro. Wrap the tortillas in damp paper towels, and heat in the microwave for 45 seconds. (Or heat them individually in a dry pan until warm and lightly toasted.) Divide the eggs, beans, cheese, and avocado among the tortillas. Roll into tight packages, and top each burrito with salsa, more cilantro, and jalapeños (if using).