Preheat the oven to 350°F (177°C).
Heat the oil in a 10-inch skillet over medium heat. Add the ground Italian sausage and break it apart with a spatula. Cook, stirring occasionally until the sausage has browned and has cooked through, about 5 minutes.
Add chopped onions, chopped green bell peppers, and minced garlic to the pan and cook for 2 minutes, stirring frequently until the onions have softened. Using a slotted spoon, scoop the sausage and vegetables onto a paper towel-lined plate to drain off the grease.
Coat the bottom of a 10-ounce ramekin with 1 tablespoon of marinara sauce.
Line the bottom of the dish with the pepperoni slices.
Add the sautéed sausage and vegetables to the dish, smoothing it out into an even layer.
Spoon the remaining marinara sauce on top of the sausage layer.
Top with shredded mozzarella cheese and place the ramekin on a rimmed baking sheet to catch any possible spills. Bake for 10 minutes.
Remove the pizza bowl from the oven and let it rest for 5 minutes before enjoying it.
