Prepare Jiffy Mix according to the instructions on the box. Once done, let it cool down.
In a large saucepan, place zucchini and yellow squash. Add enough water to just cover them.
Heat the saucepan over medium-low heat until the squash becomes tender, then take it off the heat. Drain the squash, but remember to keep one cup of the water for later.
In the same saucepan, melt all the butter over medium-low heat. Add onions and cook them until they become translucent. Then, season with salt, pepper, thyme, and parsley.
Add chicken bouillon cubes and garlic to the onions, and mix them together.
Next, add the drained squash and diced cheese to the saucepan, stirring them in.
Crumble the cooled cornbread into the squash mixture. Pour the cup of reserved water over it and mix everything well.
Spray a 13x11-inch baking pan with non-stick spray. Transfer the squash mixture into this pan.
Cover the casserole with a lid or foil and bake in an oven preheated to 350°F.
Bake for 50-60 minutes. For the last 20 minutes, remove the cover to let the top brown.
Notes
If you want to save some for later, divide the mixture into two baking dishes. Bake one and freeze the other.