Place the Tuna steaks on a plate and drizzle a good helping of olive oil on them flipping a few times to make sure they are well coated. Sprinkle with black pepper then rub the cut side of the lemon zest into the steaks (do not salt them yet).
Heat the oven to 400 degrees F and prep the veggies. For the carrots, make one cut at a 45 degree angle, then roll it 1/4 turn away from you then make another cut at the same angle. I'm not sure what this cut is called but it's great because it makes all the pieces of the carrot roughly the same thickness (which you control by how far apart you cut) so they cook evenly. I used a variety of long skinny potatoes and cut them up the same way. Then just toss the carrots, potatoes, and garlic in a good amount of olive oil, salt and pepper. Put this in the oven for about 40 minutes or until the potatoes are almost done.
Add the asparagus and carrot leaves, toss adding more olive oil if it looks like it needs it then put it back in the oven.
Take the veggies out of the oven after flipping the tuna and plate the veggies. When the tuna is done, put them on top of the veggies right away so they don't overcook. Drizzle 1 tsp of lemon juice and 1 tsp of olive oil on each steak and serve immediately.