Preheat oven to 425F. Prep baking sheet for biscuits.
Finely chop chives. Cut butter into small pieces. Whisk buttermilk powder with 1c cold water. Halve tomatoes lengthwise.
Reserve 1.5 tbsp flour. Add remaining to bowl with 1 Tbsp baking powder, ½ tsp salt, and ½ tsp baking soda. Whisk to combine. With pastry cutter, cut in butter til mix resembles pea sized crumbs. Add cheddar, buttermilk, and half the chives. Stil til just combined - dont overmix.
Scoop about ⅓c of biscuit dough onto prepared baking sheet. Bake ~15-17min, til golden brown on top and cooked through.
While biscuits bake, heat skillet over med heat with 1.5 tbsp oil and cook sausage til done.
Brush cut side of tomatoes with oil, season with salt and pepper. Broil until charred ~6-7min.
Add 2c water with reserved flour til smooth. Add all the cream cheese and flour-water mix to skillet with sausage. Cook, stirring, til cream cheese is melted and gravy thickens ~4-6min. Season with salt and pepper.
If cooking eggs, do so now. Can broil for 1-2min.
Plate biscuits, gravy, tomatoes, and egg.