Heat olive oil in a large pot over medium-high heat. Cook and stir sausage until nice and browned. Remove with slotted spoon. If using shrimp, cook in same pot (add oil if needed) for about 2-3 minutes on each side. Be careful not to overcook or shrimp will become chewy! Remove shrimp with slotted spoon and set aside. 

Add green pepper and onion to same pot in hot oil until the sausage and onion are browned, 7 to 10 minutes.

Pour water, jambalaya mix, and diced tomatoes with green chile peppers into the pot; bring the mixture to a boil, reduce heat to low, cover the pot, and simmer until the water is mostly absorbed and the rice is tender, about 20 minutes.

Add sausage and/or shrimp to the pot and continue to cook for 5 more minutes.

Serve and enjoy!