Bring a large pot of salted water to a boil. Wash and dry all produce. Core, deseed, and thinly slice green pepper. Halve, peel, and thinly slice shallot. Mince garlic.

Once water is boiling, add penne to pot. Cook until al dente, 9-11 minutes. Drain.

Meanwhile, rinse shrimp, then pat very dry with paper towels; place in a medium bowl. Toss with a large drizzle of olive oil, half the oregano, salt, and pepper. Heat a large, preferably nonstick, pan over medium-high heat. Add shrimp mixture and cook, stirring occasionally, until opaque and cooked through, 3-4 minutes. Transfer to a plate.

Heat a large drizzle of olive oil in same pan over medium-high heat. Add green pepper, shallot, and a large pinch of salt. Cook, stirring occasionally, until slightly softened, about 5 minutes. Stir in garlic, remaining oregano, and 1/4 tsp chili flakes (add more or less if you like). Cook until fragrant, 30 seconds to 1 minute.

Stir diced tomatoes and their juices, stock concentrate, and 1/2 tsp salt (1 tsp for 4 servings) into pan with veggies. Bring to a boil, then reduce heat to medium and simmer until sauce is slightly thickened, 5-7 minutes. Stir in shrimp, penne, and 2 TBSP butter (4 TBSP for 4) until combined. Turn off heat. Taste and season with salt. For a kick, add more chili flakes.

Divide pasta between bowls. Sprinkle with additional chili flakes, if desired.