Before starting, preheat your broiler to high.Wash and dry all produce. Add 10 cups water and 2 tsp salt to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. While water comes to a boil, cut tomato into 1/2-inch pieces. Cut mozzarella into 1/2-inch pieces, then season with salt and pepper. Peel, then mince or grate garlic.

Heat a large non-stick pan over medium heat. When hot, add walnuts to the dry pan. Toast, stirring often, until golden-brown, 4-5 min. (TIP: Keep your eye on them so they don't burn!) Transfer to a plate.

While walnuts toast, add penne to the boiling water. Cook, uncovered, stirring occasionally, until tender, 10-12 min. Reserve 1/4 cup pasta water (dbl for 4 ppl), then strain and return penne to the same pot, off heat.

While penne cooks, heat the same pan (from step 2) over medium. When hot, add 1 tbsp oil (dbl for 4 ppl), then onions. Cook, stirring often, until softened, 3-4 min. Add tomato sauce base, tomatoes, half the garlic and 2 tsp Italian Seasoning (dbl for 4 ppl). Cook, stirring often, until fragrant, 1-2 min. Stir in pesto, then remove from heat.

Add remaining garlic, remaining Italian Seasoning and 2 tbsp oil (dbl for 4 ppl) to a medium bowl. Add mozzarella pieces, then season with salt and pepper. Gently stir to coat. Arrange ciabatta on a baking sheet, cut-side up, then top with marinated mozzarella. Broil in the middle of the oven, until ciabatta are golden-brown and cheese is melted, 2-3 min. (TIP: Keep your eye on them so they don't burn!)

Add sauce, spinach, reserved pasta water and half the Parmesan to the large pot with penne. Stir until spinach wilts, 1-2 min. Cut garlic ciabatta into triangles. Divide pasta between plates and sprinkle walnuts and remaining Parmesan over top. Serve garlic ciabatta alongside.