Mujadarra - Black Lentils with Brown Rice and Caramelized Red Onions

black lentils, (cooked)

brown rice, (cooked)

large red onions, (thinly sliced)

garlic, (minced)

vegetable oil

salt

ground black pepper

fresh parsley, (chopped, for garnish (optional))

sour cream, (for serving (optional))