- 1 (15–16-ounce) container part-skim ricotta
- 1 (10-ounce) package frozen chopped spinach, thawed, squeezed in paper towels to remove excess moisture
- 1 garlic clove, very finely chopped
- 1 teaspoon kosher salt
- 1/4 teaspoon crushed red pepper flakes (optional)
- 1/4 teaspoon freshly ground black pepper
- 2 1/4 cups grated mozzarella (about 9 ounces), divided
- 1/2 cup grated Parmesan (about 2 ounces), divided
- 1 (24-ounce) jar marinara sauce
- 6 no-boil lasagna noodles
- 8 ounces crimini mushrooms, trimmed, sliced 1/4-inch thick, divided
- 1 tablespoon coarsely chopped flat-leaf parsley leaves
- A deep 8×8-inch microwave-proof baking dish
- Mix ricotta, spinach, garlic, salt, red pepper flakes, if using, pepper, 1 1/2 cups mozzarella, and 1/4 cup Parmesan in a large bowl.
- Spread 1/2 cup marinara evenly in bottom of baking dish. Top with 2 lasagna noodles. Coat noodles with 1/2 cup marinara. Top with half of the ricotta mixture and half of the mushrooms. Repeat with 2 noodles, 1/2 cup marinara, and remaining ricotta mixture and mushrooms.
- Top with remaining 2 noodles, sauce, and 3/4 cup mozzarella. Sprinkle with 2 Tbsp. Parmesan.
- Cover dish with parchment, then cover again with an overturned large microwave-safe plate. Microwave on high 15 minutes. Carefully check to see if noodles are tender; if not, re-cover and microwave in 1-minute bursts until tender.
- Let stand, covered, 10 minutes. Very carefully remove parchment. Sprinkle with parsley and remaining 2 Tbsp. Parmesan and serve.