Break up noodles into four to six pieces per noodle. Pieces don't have to be even.
Once water is boiling, add noodles and cook until al dente, 8-10 minutes.
Reserve ½ cup pasta cooking water*. Drain noodles in a colander, then run briefly under cold water to stop cooking the process. Set aside.
While noodles cook, prepare ingredients.
Prepare Ingredients and Cook Zucchini
Trim zucchini ends, halve lengthwise, and cut into ¼” half-moons.
Halve and peel onion. Cut halves into ¼" dice.
Place a medium oven-safe pan over medium-high heat and add 2 tsp. olive oil. You may also use a cast iron skillet. Add zucchini and red onion to hot pan. Stir often until lightly browned and tender, 3-5 minutes.
Add spinach and cook until spinach is wilted, 1 minute.
Season with a pinch of salt and pepper. Remove from burner. Remove to zucchini to a plate.
Reserve pan; no need to wipe clean.
Make the Sauce
Return pan used to cook zucchini to medium-high heat. Add marinara, cream, reserved pasta water, half the garlic (reserve remaining for garlic bread), ½ tsp. salt, and a pinch of pepper
Bring to a rolling boil and boil 1 water.
Remove from burner.
Assemble the Lasagna
Mix pasta, zucchini, and Paremsan into pan with sauce. Top with mozzarella.
Finish the Dish
Place pan with lasagna in hot oven and bake until cheese is bubbly and lightly browned, 10-12 minutes.
While lasagna bakes, halve French roll and place on prepared baking sheet, cut side up. Spread 1 tsp. olive oil and remaining garlicon rolls.
Bake until bread is golden brown, 5-6 minutes.
Serve family-style. Bon appétit!