Slice the zucchini lengthwise and peppers into large flat pieces. Toss veggies with olive oil, salt & pepper. Butter both sides of the bread.
On a hot grill pan, grill both sides of the bread. You want to have crunchy edges and grill marks on it, 2-3 minutes each side.
When you finish the bread, start grilling the zucchini strips and peppers, 3-5 minutes on each side. Again, you want grill marks and a clear softening in both vegetables.
While the veggies cook, start assembling: on two pieces of bread add a layer of brie slices, and spread the other two with mustard.
When the veggies are done, add a layer of pepper on top of the mustard, then a layer of zucchini before finishing with the cheese and bread.
Optional: fry an egg over easy and add on top of the zucchini layer.