Slice sweet potato thin, I used a mandolin slicer. Add sweet potatoes to a pot with water and bring to a boil. Reduce heat and let simmer, until sweet potatoes soften. About 5 mins.
Preheat oven to 350°F. Spray a rimmed baking sheet with cooking spray. Then place parchment on top (this will help it stick easily). Spray the top of parchement with more cooking spray and set aside.
In a skillet over medium high heat, add oil and onion. Cook until onion becomes translucent. Add in spinach and toss with onion. Let cook 2-3 minutes until spinach becomes wilted. Remove from heat.
In a bowl, beat all eggs and generously season with salt and pepper. Optionally, you can also add all eggs to a blender and blend on the lowest setting for a few quick seconds.
Pour egg into a large bowl and stir in sweet potatos, onion and spinach. Generously season with salt and pepper.
Open the oven, pull out the oven rack one notch (it should still be sturdily in place) and place the baking sheet on the rack. Then pour the omelette mixture onto the baking sheet. Use a spatula to move the vegetables around gently. Push the oven rack back into place and bake for 20-25 minutes, or until edges are golden brown and center is fully cooked.
Remove from oven and let cool. Slice into squares and serve with your favorite toppings such as hot sauce, salsa, avocado, sour cream etc.
How To Store In Fridge: This sheet pan omelet can be stored in an air tight container in the fridge for up to 1 week. These make great meal prep breakfasts or lunches!How To Store In Freezer: Let cool completely, then place the whole baking sheet in the freezer to flash freeze for 1 hour. Remove and place individual omelet slices into a freezer bag. Label bag with name and date, then seal tightly. These omelets will keep nicely in the freezer for up to 3 months.