Preheat oven to 375°F. Lightly butter either a 5" × 5" baking dish or 8-ounce ramekin. Set aside.
Place pepper halves in baking dish or ramekin. Set aside.
In an 8" skillet over medium-high heat, cook oil 30 seconds. Add onions and garlic and cook, stirring occasionally, until onions are soft and translucent, about 2 minutes.
Add spinach and cook, stirring constantly, until spinach has wilted, about 1 minute. Remove skillet from heat and set aside.
In a medium bowl, whisk together egg, cream, salt, and pepper. Stir in cooked onion mixture and cheese.
Pour mixture into pepper halves and bake 40 minutes until center is cooked.
Remove from the oven and enjoy immediately.