Chop the ends off of the zucchinis, and use a mandolin slicer or a peeler to slice the zucchinis into long, thin strips. Pat them down with paper towels to remove excess water and set aside.
Use a large, deep skillet to brown the ground beef. Season with 1/2 tsp sea salt, and set aside and drain excess fat when cooked.
Add the oil to the pan and heat. Cook the onions and garlic in the same pan on medium heat until the onions are translucent. Add in the mushrooms, zucchini slices and saute for 4-5 minutes or until soft.
Add back in the ground beef, as well as the marinara sauce, and the remainder of the seasonings. Cook for a few minutes to combine the flavors, and stir in the spinach at the very end. Stir until the spinach has wilted.
Top with sliced grape tomatoes (omit for AIP), extra seasoning to taste, and serve!