Note: This stew appeals to those who are feeling meat-deprived, and tastes great to the rest of us. Substitute all you like. The secret is in browning everything, which requires some time and attention, but then it just cooks itself and makes the house smell wonderful.
Break the burgers into chunks, and brown in a little oil. Set aside. Cut the carrots and celery into chunks, coarsly chop the onion, brown in batches and set aside. Slice the shrooms and brown them. Throw in the garlic, minced, for the last couple of minutes.
Now dump everything back into the pot (a heavy dutch oven is just the thing) and cover with water. Bring to a boil, and while it is heating up, add the various gravy seasonings (don't overdo the tomato). Mix a thin paste with a little cold water and about 3 Tbsp. flour. Stir this into the hot liquid a little at a time until it is not-quite-thick-enough (it will cook down some). Add the potatoes, quartered, and the green beans. Lower the heat and simmer for a half hour or so, until the potatoes are just done. Thicken or thin the gravy and correct the seasonings.
Serve with biscuits and salad for a great fall dinner.
Gravy note: The best gravy is made by mixing the flour into fat, either in the pot and browning it a bit, or as a roux (blending into a paste with margarine). But with so many other flavors, who cares how the flour is handled!