Preheat oven to 350°F. Grease a muffin pan and set aside.
In a large bowl, beat together eggs, salt and pepper until blended. Stir in the Parmesan cheese.
Heat a skillet over medium heat. Add the oil and onions and cook for about 3-4 minutes, until onions are golden. Add the sweet potatoes and thyme. Cover and cook for 8 more minutes, stirring occasionally, until the potatoes begin to soften.
Add the red bell pepper and cook 4 minutes more. Stir in the prosciutto. Add the spinach and cook for 2-3 minutes, until wilted. Lastly, add the garlic and cook for another 1 minute. Spoon the vegetable mixture into the muffin pan, distributing it evenly. Top every one with 3-4 tablespoons of the egg and cheese mixture. Bake for 15-20 minutes, until lightly browned.
Let cool for few minutes and remove your individual frittatas from the muffin pan. Enjoy!