Heat up the oil in heavy skillet. It should be 1-2 inches deep. I think there's an ideal frying temperature (375F?) but I forget. Cook the shallots in oil until they turn golden and a bit crispy. Spread them on a pile of paper towels to drain. Probably need to do batches unless your pan is big. Add some salt and let them cool. Don't eat them all as a snack.
Chop the bacon into 1/4" bits and fry until just crispy. Set aside.
Mince the mushrooms into 1/4" bits. I liked the suggestion to smash them with a heavy pan before chopping.
Combine chicken stock, lemon juice, soy sauce, and cream. Set aside.
Fry the mushrooms in the bacon grease (add butter if needed) on high until the liquid is evaporated, the turn down the heat and add garlic and cook for a minute. Add flour and cook, stirring constantly, until the flour becomes golden. Dump in the chicken stock mixture and cook, whisking constantly, until it's about the same thickness as that can of cream of mushroom soup we're trying to avoid using. Season with salt and pepper.
Bring some water to boil while you prep the green beans, chopping them into 1-2" sections. Blanch the beans in batches, then plunge into ice water. Drain, then dump into mushroom mixture.
Add 1 cup of shallots to mushroom mixture, then pour into a 9x13 casserole dish. Bake at 350F for about 20 minutes. Top the dish with the panko and the rest of the shallots if they haven't all been eaten by this point. Continue cooking for another few minutes until bubbling.