Taco toppings are what makes each one unique. If restricting potassium, a few ingredients to be mindful of the portion size for are avocado and salsa. Diced tomato or even pico de gallo have far less potassium than prepared salsa. Fun toppings can include feta, picked or raw red onion, fresh peppers, a dash of hot sauce. Fresh cilantro can be a great addition but is also polarizing so if serving for a group, consider having it on the side. Some people have a soapy flavor when tasting cilantro while others do not.
Don’t forget a source of acid with your tacos! Acidity helps to balance out all the delicious flavors! Sources of acid could be a lime wedge, pickled veggies like onion or jalapeno (be sure to check the sodium content if store bought), or hot sauce.