Preheat oven to 375 degrees F.

In large skillet over medium-low heat, heat olive oil. Cook onions, stirring occasionally, until deeply browned, about 45 minutes.

Meanwhile, bring large pot of salted water to boil. Add green beans; cook 4 minutes. Drain well. Set aside.

Add minced garlic to pan with caramelized onions. Continue cooking until fragrant, 30 seconds to 1 minute. Add chickpea flour, tamari, vegetable stock, nutritional yeast, rosemary, salt and pepper. Stir to combine.

Raise heat and bring to simmer. Let simmer, stirring often, 5 minutes or until mixture has noticeably thickened.

Transfer to 9”x9” baking dish. Stir in cooked green beans until completely combined. Sprinkle chopped walnuts evenly over surface of casserole.

Bake, uncovered, 20 minutes or until walnuts are slightly golden and mixture is bubbling at edges. Let cool 5 to 10 minutes before serving.