If the sirloin steak tips aren't cut into 2 to 3 inch pieces, go ahead and cut them up evenly. This makes them cook like traditional steak tips, but they do require more tending on the grill. If you're in a rush or feeling lazy then you can cook the steak tips whole and slice them after cooking. You won't get a nice char on all sides of each piece and you will definitely need to let the pieces rest before cutting or you'll lose all the juices.
Place steak tips into a plastic zipper bag along with the 1/2 cup of yogurt, 1 tsp of onion powder, 1tsp of garlic powder, and 1/2 teaspoon of coarse crushed pepper. Seal the bag with a lot of air in it and shake up the bag or rotate the contents to get all of the steak tips covered in the marinade.
When the steak tips are well covered, open the bag, carefully squeeze out the air, and reseal it. Place it in the refrigerator for at least 4 or up to 8 hours before cooking to allow the yogurt to tenderize the meat. Flip the bag over onto the other side, halfway through the marination time.
Roughly 30 minutes to an hour before you are ready to grill, take the steak tips out of the refrigerator and let them sit at room temp until ready to grill.
Get the grill very hot on high to medium-high heat (roughly 500 - 600 degrees F when the lid is closed). Place each of the steak tips on the grill using tongs and sprinkle some kosher salt over them quickly before closing the lid. Grill them for 4 minutes before opening the lid, flipping them, and grilling for another 3 minutes for medium. (Cook them 3 minutes on one side and 2 or three minutes on the other side for medium rare).
Remove the steak tips and place them on a large plate or serving dish. Let the steak tips rest for 10 minutes before serving to allow a redistribution of the juices.
Serve them up with your favorite veggies, rice, mashed potatoes, or with a side of your favorite sauce. They go wonderfully with barbecue sauce, ranch, or hot sauce, but are more than excellent on their own!