Slice the tomatoes into wedges, about 8 wedges per tomato. Arrange them on a cutting board or plate and generously sprinkle with kosher salt. Set aside in the fridge to chill and release excess moisture. This can be stored ahead for up to 12 hours.
Add the boursin, buttermilk, mayo, lemon zest, onion powder, pepper, and chives to a medium bowl and whisk until smooth, about 3-5 minutes. The boursin may need time to dissolve into the buttermilk, so keep whisking. You can make this 1 day in advance of serving.
Finely chop the bacon slices and place them in a skillet over medium heat. Fry the bacon bits for 2 minutes, until some of the fat releases. Crush the crispy fried onions in your hands into the skillet. Fry the onions and bacon bits together for 5-6 minutes, or until the bacon appears crispy and the onions have turned a deeper golden brown.
Assemble: Spoon the dressing onto a serving platter. Add the tomato wedges, letting excess moisture drip off each tomato wedge before adding to the platter. Sprinkle extra chives and all the bacon onion bits on top right before serving.