Spread walnuts on a baking sheet and roast in the oven for 10 minutes. Allow to cool slightly, then transfer the walnuts to a food processor.
Add beans, tahini, maple syrup, and salt to the food processor and blend. Slowly add water until the mixture is thin enough to drizzle. Set mixture aside.
In a large sauté pan, add olive oil and shallots. Sauté over medium heat. Add mushrooms and peppers and sauté for 10 minutes. Add the greens, toss with other ingredients and sauté until greens begin to wilt. Add mirin and tamari, cover and simmer on low heat for 5 minutes.
To serve, place a generous serving of the greens on a plate and drizzle the walnut sauce over the top.