Preheat oven to 500°. Bring a pot of salted water to boil. Peel carrots & cut at alternating angles into 1 1/2" pieces.
Place the carrots on a baking sheet & drizzle with about 2 tsp olive oil. Season with salt and pepper and toss to thoroughly coat. Roast 10-12 minutes, or until browned and tender when pierced with a knife.
On a separate baking sheet, toss tatsoi with about 2 tsp olive oil & salt and pepper. Roast 6-7 minutes, until browned and tender.
Once he water is boiling, add the couscous. Cook for 5-6 minutes, or until completely tender. Drain well and return to the pot. Stir in the juice of 2 lime wedges and a drizzle of olive oil. Season with salt and pepper to tasted.
Pat the fish fillets dry and season with salt and pepper. Gently dip the fillets in the flour to create a thin coating, shaking off any excess. In a medium nonstick pan, heat a little olive oil on medium-high until hot. Cook the fillet 4-5 minutes per side, or until golden brown and cooked through. Transfer to a plate and wipe out the pan.
In the same pan, heat a little olive oil on medium-high until hot. Add the shallot and season with salt and pepper. Cook for 1 minute, or until slightly softened. Add the lime zest and 1/4 cup of water. Turn off the heat, leaving the pan on the burner. Working in 3 batches, slowly whisk in the butter until completely combined and smooth. Stir in the juice of the remaining lime wedges and set aside
Just before serving, stir the mint into the couscous. To plate, divide couscous, roasted vegetables, and cod between 2 plates. Spoon the butter sauce over the top & enjoy.