Tajin is my current topping obsession. Sometimes it's a certain hot sauce or a mustard, but whatever it is, it goes on everything. The food doesn't taste quite right without it. I know I'm not the only one. Tajin was first introduced to me through Trader Joe's. TJ's has a Chili Lime spice blend (next to the Everything but the Bagel seasoning) that's almost the same.
But Tajin is the OG, can be bought on Amazon and in larger quantities so that's your best bet. There are essentially no calories, so sprinkle away. My list of things to put Tajin on is ever-expanding, but my favorites are:
-Salads (like this grilled salmon salad)
The rim of a spicy margarita