Warm the pot: Heat a large, deep skillet or Dutch oven over medium. Add 1–2 tablespoons olive oil and 1 tablespoon butter (if using).
Sauté aromatics: Add onion and a pinch of salt.
Cook 3–4 minutes until translucent. Stir in garlic and cook 30 seconds until fragrant.
Add vegetables: Stir in carrots, bell pepper, and mushrooms. Cook 4–5 minutes, stirring occasionally, until they soften and the mushrooms release moisture.
Toast the orzo: Add the dry orzo to the pot.
Stir for 1–2 minutes so it lightly toasts and picks up flavor.
Season: Sprinkle in 1 teaspoon Italian seasoning (or 1/2 teaspoon dried thyme), 1/4–1/2 teaspoon red pepper flakes, and several grinds of black pepper. Adjust salt to taste, keeping in mind the broth and cheese.
Add broth: Pour in 4 cups vegetable broth and bring to a gentle simmer. Reduce heat to medium-low and cook, stirring frequently to prevent sticking, for 9–12 minutes.
Stir in greens and peas: When the orzo is almost al dente and the liquid is mostly absorbed, add spinach or kale and the frozen peas.
Cook 2–3 minutes until the greens wilt and peas are heated through.
Make it creamy: Remove from heat. Stir in cream or Greek yogurt and half the Parmesan (if using). Add lemon zest and a squeeze of lemon juice.
If it seems too thick, splash in more warm broth or hot water to loosen.
Taste and finish: Adjust salt, pepper, and lemon. Top with remaining cheese or nutritional yeast and chopped herbs.
Serve hot: Spoon into bowls and drizzle with a little olive oil. Add extra red pepper flakes if you like heat.