Cut potato into ¾" dice. Heat 2 Tbsp. olive oil in a large oven-safe pan over medium-high heat. Add potato to hot pan and stir 1 minute. Reduce heat to medium, and cook 5 minutes, stirring once halfway through. Place pan in oven, and roast until golden brown and tender, 20-22 minutes, stirring halfway through. Remove from oven, season with ¼ tsp. salt and a pinch of pepper. While potatoes roast, prepare ingredients.
Prepare the Ingredients
Mince garlic. Stem and mince parsley. Trim ends off green beans. Pat cod dry, and season with a pinch of salt and pepper.
Make the Sauce
Heat a small pan over medium heat. Add 1 tsp. olive oil, half the garlic (reserve remaining for green beans), and red pepper flakes (to taste). Cook until aromatic, 30-60 seconds. Stir in marinara and bring sauce to a gentle boil, 2-3 minutes. Remove from burner, and stir in half the parsley (reserve remaining for garnish).
Cook the Fish
Place a medium non-stick pan over medium-high heat. Add 1 tsp. olive oil and cod to hot pan. Cook undisturbed until lightly browned and cod reaches an internal temperature of 145 degrees, 4-5 minutes per side. Transfer to a plate. Reserve pan, and wipe clean.
Finish the Dish
Return pan used to cook cod to medium heat. Add 1 tsp. olive oil, green beans, and remaining garlic to hot pan. Cook until aromatic, 30-60 seconds. Add 2 Tbsp. water, cover, and cook until bright green and tender, 2-3 minutes. Season with a pinch of salt and pepper. Spoon ¼ cup sauce on plate and top with potatoes. Place green beans then cod on potatoes. Cover with remaining sauce, and garnish with remaining parsley.