Bring a large pot of salted water to a boil. Cook the linguine according to package directions until al dente. Reserve 2 cups of the pasta water before draining then and set aside.
Pat scallops dry with paper towels. remove the membrane on the side. Season both sides with salt and pepper, then lightly coat with flour.
In a large sauté pan, heat the olive oil and butter over medium-high heat. Add scallops and sear for about 3 minutes per side until golden brown and cooked through. Remove and set aside.
In the same pan, add a little more oil if needed. Sauté the chopped onion and garlic until softened and translucent, about 3–4 minutes.
Pour in the chicken stock or white wine to deglaze the pan, scraping up any brown bits. Stir in the marinara sauce, reserved pasta water and heavy cream. Simmer for about 10 minutes, or until the sauce thickens.
Add the chopped spinach and fresh herbs during the last 5 minutes of simmering. Stir to combine and let the spinach wilt.
Toss the cooked linguine in the sauce until well coated. Plate the pasta, top with seared scallops, and garnish with grated Parmesan and a sprinkle of fresh