These are killer.

Feta cheese off of a block, cut into cubes to fit tomatoes
3 tablespoons extra-virgin olive oil plus additional for drizzling
1 tablespoon Balsamic vinegar
1.5 tablespoon minced shallot
1/2-3/4 teaspoon chopped fresh oregano, or dried, to taste
12-18 large cherry tomatoes
12-18 pitted Kalamata olives, halved lengthwise

Toss cubed feta, oil, vinegar, shallot, and oregano in small bowl. Season with salt and pepper. Let marinade for at least an hour.
Cut tomatoes in half, across the equator. Scoop out tomato pulp with melon baller or small spoon, turn upside down for a few minutes on paper towel to drain.
Place tomatoes, cut side up, on serving plate. Sprinkle with salt and pepper.
Stuff hollowed cherry tomatoes with marinated feta.
Slide in olive half alongside cheese.
Drizzle with additional olive oil or marinade.
Do ahead: Can be made 6 hours ahead. Cover and chill.

I use no salt, and added the Balsamic vinegar to the recipe, I like a 3:1 oil to vinegar ratio. Cut the feta into whatever size will fit the tomatoes you have, enough to leave a bit of room for the olives. Also rather than drizzle with plain olive oil I use the marinade. The longer you marinade the feta the betta, an hour is fine but I like to go overnight. I've left the feta cubes in the marinade for a week, the feta won't get mushy, it softens just bit but it's still plenty firm. Keep the feta/marinade mix refrigerated if marinading overnight, and pull out an hour so ahead as the olive oil hardens. I've nuked it for about 5 secs or so if in a rush to melt the oil.

I've had them the next day and they are still fine, the tomatoes soften a bit and lose some flavor when refrigerated but they are still good with all of the other stuff in there.

You can stabilize them with a toothpick put in at an angle, and to make them less messy to eat. For home I don't, if taking them somewhere they transport better that way.