Pre-heat oven to 350 degrees and have a deep lasagna size baking dish ready.
Cook farro according to package instructions and place cooked farro in a large bowl; set aside.
Heat a deep skillet over medium-high heat. Remove sausage from casings and add to pan along with the garlic. Saute until golden brown and cooked through, about 7-9 minutes, stirring frequently. Using a slotted spoon, remove sausage from pan and place in the bowl with the reserved farro.
Add the butternut squash cubes to the hot pan and sauté in the remaining fat rendered from the sausage.
Sprinkle with salt and pepper to taste and sauté until squash becomes fork tender, about 4-5 minutes.
Stir in spinach during the last minute of cook time. Remove from heat and place cooked squash and wilted spinach to the bowl with the farro and sausage.
Return to the bowl with the farro mixture and stir in the fire roasted diced tomatoes, roasted red peppers and shredded mozzarella.
Check for seasoning and add salt and pepper to taste. Spread mixture into the baking pan and top with fresh mozzarella slices.
Bake until warm and cheese is golden brown and bubbly, about 45 minutes. Sprinkle with parmesan cheese to serve if you wish.