Preheat oven to 350°
Grease or line a 12 cup muffin tin or 5 glass oven safe meal prep containers and set aside for now
In a large bowl, whisk 10 large eggs with 1/2 cup of your favorite milk, 1/2 teaspoon of salt and a pinch of black pepper and set aside for now
Place a large skillet over medium heat and crisp up 8 strips of diced bacon
Transfer the crispy bacon onto a paper towel lined plate and set aside for now
Discard most of the bacon fat out of the skillet and place the skillet back over medium heat
Add the spinach into the skillet, cover and cook until wilted
Add the crispy bacon, wilted spinach, a cup of diced tomatoes and 1/2 cup of shredded cheese in with the whisked eggs, season with salt and black pepper and mix until everything is evenly distributed
Divide the mixture evenly into the greased containers and bake in a 350° oven for 20 minutes (cupcake tins) or 25 minutes for larger containers
As soon as the center of the frittatas feel springy, transfer them onto a heat proof surface to cool
Serve while warm or chill until ready to enjoy