Bring a large pot of lightly salted water to a boil. Add linguini pasta, and cook for 6 to 8 minutes, or until al dente. Drain.

In a skillet, saute the red onion and garlic powder in olive oil until onion is translucent. Add the milk and cook until bubbles form around the edges of the pan.

Add parsley, green bell pepper, red bell pepper, broccoli, carrots, mushrooms, shrimp, crab, and scallops. Stir until well incorporated.

Remove 1/2 cup of milk, stir it with flour in a small bowl until smooth, then add back to the skillet to thicken the mixture. Season with salt and pepper.