How to fill a big hole (with wood filler)

So we're in the process of rehabbing the kitchen, slowly. Directly to the left of my (gas) range is where the original wall oven unit used to be. I know there used to be a wall unit because my neighbor has the same kitchen and his is still functional. Some previous owner replaced the oven/cooktop with a range. The oven space was converted to countertop, which I suspect is a huge improvement in functionality compared to the original (no counters directly adjacent to the cooktop - what were the builders thinking?). Whomever did the upgrade was pretty sloppy - none of the cuts were straight... and there was a chunk missing just to the left of the range hood (which we are in the process of replacing).  See?

If I used wood filler alone, the suff would fall back into the hole. What I needed was a way to provide support for the filler....

After filling and sanding (and a little painting). Obviously it needs more work, but a step in the right direction!