Heat the oil in a large sauté pan over medium-high heat; add the onions and cook until golden brown. Stir in the tomatoes with the salt and pepper and remove from the heat.
Boil the lentils, the rice and the fettuccine separately in pots of water until cooked. As each one cooks, drain and add to the tomato mixture; set aside.
Melt the butter in another large pan. Add the shrimp, mint, salt and pepper. Sauté for 2 to 3 minutes until the shrimp has turned a light pink. Serve immediately on top of the tomato-lentil mixture.