Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Halve potatoes lengthwise; slice crosswise into ¼-inch-thick half-moons. Halve, core, and thinly slice bell pepper into strips. Trim and thinly slice mushrooms (skip this step if your mushrooms are pre-sliced!). Peel and mince or grate garlic.

Toss potatoes and bell pepper on a baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack until browned and tender, 18-20 minutes.

Meanwhile, pat pork* dry with paper towels and season all over with salt and pepper.

Heat a drizzle of oil in a large pan over medium-high heat. Add pork; cook until browned and cooked through, 4-6 minutes per side.

Turn off heat; transfer to a cutting board to rest. Wipe out pan. TIP: Tent pork with foil to keep warm until ready to serve.

Swap in chicken* for pork. Cook until browned and cooked through, 3-5 minutes per side.

Heat a drizzle of oil in pan used for pork over medium-high heat. Add mushrooms; cook, stirring occasionally, until lightly browned and slightly crispy, 2-3 minutes. Season with salt and pepper.

Add garlic; cook, stirring occasionally, until garlic is fragrant and mushrooms are browned and crispy, 1-2 minutes more.

Stir marinara, stock concentrate, and ½ cup water (¾ cup for 4 servings) into pan with mushroom mixture. Bring to a simmer; cook until sauce thickens slightly, 1-2 minutes.

Remove from heat; stir in 1 TBSP butter (2 TBSP for 4) until melted.

Slice pork crosswise.

Divide pork and roasted veggies between plates. Spoon mushroom marinara over pork and serve.

Slice chicken crosswise.