Preheat your oven to 400°F and grease a 9x13-inch baking dish.
Heat the oil in a large skillet over medium heat. Add the carrot and onion, and sauté for 3 minutes, or until crisp tender. Add the green beans, brussels sprouts, and cauliflower, and sauté for 3 minutes. Then add the mushrooms, and sauté for 3 minute. And add the arugula, and cook for 2 minutes, or until the leaves are welted.
Add the lemon juice to your vegetables, and cook for 1 minute, or until most of the liquid is absorbed. Add the flour and stir as it cooks for 2 minutes. Slowly whisk in the stock until the flour is combined and the sauce is smooth. Cook, for 2 minutes, while stirring, until thickened. Stir in the coconut milk, salt, and pepper, and cook while stirring for 3 minutes, or until the mixture is thickened.
Spread the vegetable mixture into your prepared baking dish. Evenly sprinkle the top with the crispy fried onions.
Bake the casserole for 20 minutes or until it is heated through and the top is golden brown.
Makes about 10 cups.
Notes
Options: You can use regular canned coconut milk for richer, or lite canned coconut milk for saucier. Or, instead of the coconut milk, you can use 1 cup unsweetened dairy-free milk beverage + ¾ cup dairy-free heavy cream alternative. Look for coconut cream, brands like Silk, Country Crock, or Califia Farms, or make your own Heavy Cashew Cream.