Whisk the sour cream, buttermilk, garlic powder, and onion powder, salt and pepper in a large bowl until smooth.
Halve the avocados and discard the pits. Scoop the avocados into the bowl with the dressing and mash them up with the dressing to desired chunkiness. Stir in tomatoes, onion, chives, and parsley. Season more with salt and pepper if needed.
Can make this 4-6 ahead of time. Lightly cover and refrigerate. The buttermilk and sour cream will help to prevent discoloration. Serve with tortilla chips.