Preheat oven to 450 degrees. Combine 4 tbs olive oil, juice of ½ lemon juice, 1/2 tsp salt, 1/4 tsp pepper, 1/4 tsp oregano, 1/4 tsp thyme, 1/4 tsp basil, and 1/2 tsp garlic powder in a large resealable bag along with 4 tuna fillets. Seal the bag, massage the fillets to rub in the seasonings and distribute all the ingredients. Chill for 15 minutes while you move on to the next step. In a large bowl combine 1 ½ lbs baby red potatoes halved and 2 tbsp olive oil and toss to coat. Stir together ½ tsp salt, ¼ tsp pepper, ¼ tsp oregano, ¼ tsp thyme, ¼ tsp basil, and ½ tsp garlic powder, sprinkle over potatoes and stir to combine. Arrange potatoes on half of a greased sheet pan. Bake for 15 minutes. After 15 minutes, place tuna fillets on the empty half of the sheet pan (add lemon slices if desired), sprinkle 4 tbsp grated parmesan cheese over the potatoes, and return to the oven for 6 minutes. Flip the tuna fillets, and cook for another 6 minutes. Serve and enjoy!