Pulse garlic bread in food processor until you have fine crumbs, then toast in large, shallow Dutch oven over medium heat until lightly golden and crisp. Transfer crumbs to small bowl.
Drizzle olive oil into Dutch oven and place back over medium heat. Add broccoli stems, scallions and garlic, followed 2 minutes later by half the peas and all the spinach.
Season with a pinch each of sea salt and black pepper, then cook for 10 minutes or until veg is soft and spinach has thawed, stirring regularly.
Meanwhile, cook pasta in large pot of boiling salted water following package instructions, adding broccoli florets and remaining peas for the last 3 minutes.
Scoop 1 cup starchy cooking water from pasta pot and stir into vegetables along with cheese, then blitz carefully with an immersion blender until smooth.
Drain pasta, broccoli and peas, toss with sauce and spoon into bowls, finishing with a fine grating of cheese. Serve the garlicky bread crumbs alongside for sprinkling.