• Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Line a baking sheet with foil (line 2 sheets for 4). Wash and dry produce. • Trim any large stems from portobello mushrooms if necessary.

• Drizzle both sides of each mushroom with olive oil; rub to evenly coat. Season all over with 1 tsp Italian Seasoning (2 tsp for 4 servings), salt, and pepper. (You’ll use the remaining Italian Seasoning later.) Arrange mushrooms gill sides down on prepared baking sheet. (Divide between both prepared sheets for 4; roast on top and middle racks.) • Roast on top rack until tender, 14-16 minutes.

• Once water is boiling, add spaghetti to pot. Cook until al dente, 9-11 minutes. • Reserve 1/2 cup pasta cooking water, then drain.

• Meanwhile, melt 1 TBSP butter (2 TBSP for 4 servings) in a large pan over medium-high heat. Add panko and half the garlic powder. Cook, stirring, until golden brown, 3-5 minutes. Season with salt and pepper. Turn off heat; transfer to a small bowl. Wipe out pan. • Return same pan to medium heat. Pour in marinara, remaining Italian Seasoning, remaining garlic powder, stock concentrate, 1 tsp sugar (2 tsp for 4), and a pinch of chili flakes if desired. Bring to a simmer; cook, stirring occasionally, until warmed through, 2-3 minutes. • Turn off heat. Reserve 1/4 cup marinara (1/2 cup for 4).

• Once mushrooms are tender, remove sheet from oven; flip mushrooms over on sheet. Heat broiler to high. • Stir drained spaghetti and 1 TBSP butter into sauce. • Spoon reserved marinara into mushrooms, then mound evenly with Italian cheese. • Broil until cheese is melted and lightly browned, 2-4 minutes. TIP: Watch carefully to avoid burning.

• If needed, stir reserved pasta cooking water a splash at a time into pan with spaghetti over low heat until pasta is thoroughly coated in sauce. Taste and season with salt and pepper. • Divide spaghetti between plates and top with cheesy mushrooms. Sprinkle with toasted breadcrumbs and remaining chili flakes to taste. Serve.