Definitely flavor each aspect individually. And technically, if you're putting rice in it, it's not a taco. You may be holding it like a taco, but it's heresy to put rice in a taco.
Plain rice, beans or steak are all going to offer very little in the way of flavor. If you're dealing with leftovers, this is what I do:
Rice - Starting with cold rice, pour a little fat (lard is great, but butter would work too) into a pan, add a hefty sprinkling of chili powder, a handful of chopped onion and some garlic. And a healthy dose of salt. (At the very least - pepper, cayenne, chipotle, cumin, coriander, oregano all will go beautifully here also.) Heat it until you smell it, then dump in your rice, and give it a good stir. Add maybe 1/4 c of water to the pan, pop a lid on it, and turn it down to the lowest setting, let it heat for 5-10 min.
Beans - Starting with cold beans, pour a hefty amount of fat (again, lard) into a skillet, toss in some chopped onion and garlic, heat until the onions are translucent, dump in your beans, add plenty of salt, pepper, etc (all the same spices as above will work), and mash with the back of a fork as they heat up. If there's excess liquid, just let it simmer until they're a good consistency. If they're too dry, add some water/stock and a fair bit of fat.
Steak - Again, assuming leftovers, chop it up into whatever bits you're planning to use, then toss with the above spices. Heat quickly in a hot pan.
My "Mexican Spice Mix" is just Coriander, Cumin, Chili Powder mixed to the right smell (it sounds weird, but it really works). You can add oregano and salt if you like, but I add them separately. But the flavor combo adds a distinctive flavor to any dish.
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), sliced flank steak marinated in Mojo
and cooked on the rare side, fresh pico de gallo or homemade salsa, guacamole or avocado slices, and a spritz of fresh lime juice.
