Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Trim the woody ends off the asparagus and toss the spears with half of the olive oil, salt, and pepper.
Roast the asparagus in the oven for 10 to 12 minutes until tender and slightly charred.
While the asparagus roasts, steam the cauliflower florets until they are very soft and easily pierced with a fork.
Transfer the steamed cauliflower to a blender or food processor with the minced garlic and a pinch of salt, then process until smooth and creamy.
Pat the cod fillet dry with a paper towel and season both sides with salt and pepper.
Heat the remaining olive oil in a non-stick skillet over medium-high heat.
Sear the cod for about 3 to 4 minutes per side until the fish is opaque and flakes easily.
Plate the cauliflower mash first, top with the seared cod, and serve the roasted asparagus on the side.
Drizzle the entire dish with fresh lemon juice before serving.