Meaty tacos are great, but who doesn't love charred sweet asparagus in the springtime? I like to cook mine in olive oil until nearly blackened in spots so that you get a nice contrast between the natural sweetness of the 'gus and the smoky, browned complexity of the charred spots. If you've got a real grill burning charcoal, all the better.
The key to getting your asparagus to work in taco form is to cut it into pieces that are small enough that you don't drag whole stalks out of the tortilla as you bite in, but still large enough that you get a good meaty bite when you shove that folded double-stacked tortilla in your mouth.
If you're lucky enough to live near a farmers' market or good supermarket, now's the time to try out as many different types of asparagus as possible. Slender, sweet green stalks are delicious, but their fatter, meatier purple cousins are great as well. The Spanish specialty white asparagus is grown with dirt piled on top of it, completely depriving it of sunlight—a process called etiolation. Without sunlight, the stalks form no chlorophyll and stay a ghostly white. They're getting easier to come by in the states these days and boast a delicately bitter flavor and mild sweetness.
I like to use a mix of stalks to give some complexity to my tacos.
For condiments, you could go with a bright green salsa verde if the asparagus isn't already enough green for you (I like to cut mine with a bit of sour cream to add a touch of richness to the taco), or when the good tomatoes start coming in, a nice roasted tomato salsa would also be a fine choice. In this case, I happened to have some homemade adobo sauce left over from when I made Beef Barbacoa Tacos last week. After combining it with some sour cream, its rich, roasted chili flavor paired so perfectly with the asparagus that I think it's worth making a separate batch for your asparagus tacos even if you don't have leftovers sitting around in your fridge like I did.
The base for the adobo sauce is roasted whole chilies along with a few canned chipotles. I use a few different types of dried chilis to add some complexity to the finished dish, but if you're looking for a quicker, easier, no-cook alternative, simply blending together some canned chipotles with equal parts sour cream and a squeeze of lime juice makes a fine taco condiment.
Additional garnishes are totally at your discretion, but might I recommend some pickled red onions, chopped cilantro, and some crumbled queso fresco or cotija cheese?
Seriously—make these at your next cookout, and I guarantee that nobody will ask you where the burgers are.