Keto Taco Casserole

Preheat oven to 350°. In a large skillet over medium heat, heat oil. Add onion and cook until slightly softened, 2 minutes.  Add ground beef and season with salt and pepper. Cook, breaking up meat with a wooden spoon, until no longer pink, 6 minutes. Sprinkle in taco seasoning and jalapeño and cook, stirring, until spices are lightly toasted, 1 minute. Drain and let cool slightly.  In a large mixing bowl, whisk eggs, then add in meat mixture. Spread mixture into an even layer in the bottom of a 2-quart baking dish. Sprinkle with cheese.  Bake until set, about 25 minutes.  Sprinkle with parsley and top each slice with a dollop of sour cream and jalapeño, if desired.