Step 1
Preheat oven to 275 degrees F (135 degrees C). Spread almonds on a baking sheet.
Step 2
Toast almonds in the preheated oven until golden stirring halfway through about 13 minutes total. Remove from oven and set aside.
Step 3
Increase oven temperature to 350 degrees F (175 degrees C). Grease one 9x13-inch casserole dish.
Step 4
Place bacon and onion in a large skillet and cook over medium-high heat turning occasionally until evenly browned 8 to 10 minutes. Remove bacon and onion with a slotted spoon; set aside. Drain excess bacon fat from the skillet; add olive oil. Add mushrooms and cook stirring until soft about 5 minutes.
Step 5
Place 1 quart water in a saucepan and bring to a boil. Add green beans and blanch for 2 minutes. Drain in a colander and immediately immerse in ice water for several minutes to stop the cooking process and preserve the bright green color. Drain.
Step 6
Pour mushroom soup into a large bowl and whisk until smooth adding up to 1/2 cup water until soup is the consistency of thick gravy. Stir in almonds 3/4 of the bacon-onion mixture (reserving the rest for topping) mushrooms green beans 1 cup French-fried onions and water chestnuts. Mix thoroughly to combine and season with salt and black pepper.
Step 7
Pour green bean mixture into casserole dish. Top with remaining bacon-onion mixture and 1 cup French-fried onions.
Step 8
Bake in the preheated oven until bubbling and crispy on top 30 to 45 minutes. Serve hot.