Pour the contents of the 6.5 oz jar of roasted peppers (including the liquid) into a blender, food processor, or tall container for an immersion blender and puree until smooth. Set aside.

Fill a large pot with water and bring it to a rolling boil; add salt to taste.

Heat 3 tbsp olive oil in a large skillet over medium heat. Add the 1 small diced onion and sauté until soft and translucent, about 7–10 minutes.

Add the 2 minced garlic cloves to the skillet and cook, stirring, for 1 minute.

Add the 1 lb sliced mushrooms to the skillet. Cook, stirring occasionally, until the mushrooms release their liquid and begin to brown, about 8–10 minutes.

Stir in the pureed roasted peppers, 1 tsp dried Italian herbs, 1 tsp pepper, 1/4 tsp red pepper flakes (optional), and salt to taste. Bring the mixture to a gentle simmer.

Add the 1 lb calamari rings (fresh or thawed) to the skillet. Cook over medium heat until the calamari are just opaque and tender, about 3–5 minutes; avoid overcooking.

While the calamari are cooking (or immediately after starting them), add the 1 16 oz package of fettuccine to the boiling water and cook according to package instructions. Before draining, reserve some of the pasta cooking water, then drain the fettuccine (do not rinse) and set aside.

Reduce the skillet heat to low and stir in 1 cup Half & Half or heavy cream. Warm the sauce gently, stirring until combined and slightly thickened, about 1–2 minutes. Turn off the heat.

Add the drained fettuccine to the skillet and toss to combine. If the sauce seems too thick, add a little of the reserved pasta cooking water to loosen it and coat the pasta evenly.

Taste and adjust salt and pepper if needed. Serve immediately, garnished with chopped parsley.