Preheat oven to 350 degrees.  Fill a large stock pot with water and bring to a boil.  Add tortellini and cook according to package instructions.

Place bacon in a medium sized skillet on the stove-top at medium-high heat.  Cook until crisp.  Remove bacon from pan with slotted spoon and set on paper towels to drain.  Reserve two tablespoons bacon drippings in pan and discard the rest.  Add garlic to pan and cook until fragrant and tender, about 1 minute.  Add flour to pan and stir with a whisk for about 1 minute. Slowly add milk and continue to stir with whisk until smooth.  Add salt, pepper, basil, and red pepper flakes and bring sauce to a simmer.

While sauce is heating, use a microplane grater or a fine-holed cheese grater to zest lemon.  Then cut lemon in half and remove juice.  Add 2 teaspoons zest and 1 tablespoon lemon juice to sauce.  (Note:  I really love lemon so I added this to my tastes.  If you don’t want as strong of a lemon flavor, I suggest cutting it down to 1 teaspoon zest and 2 teaspoons lemon juice) .  Continue to stir until thickened, 2-3 minutes.  Remove from heat.

Drain tortellini and place back in stock pot.  Reserve 1 tablespoon of the cooked bacon and add the rest to the pasta mixture.  Add spinach, 1/2 cup mozzarella cheese and 1/2 cup Parmesan cheese.  Add sauce and gently stir to combine.  Place pasta mixture in an 8×8 or 9×9 baking dish and top with remaining 1/4 cup mozarella and 1/4 cup parmesan and also crumbled bacon.

Cover pan with foil and bake for 20 minutes.  Remove foil and bake for an additional 5-10 minutes, until cheese on top is melted and pasta is bubbly throughout.  Remove from oven and cool for 10 minutes before serving.