Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the onion and garlic and cook for about 4 minutes, until fragrant and the onion is translucent.
Add the apples, mushrooms, fennel seeds, rosemary, sage, maple syrup, salt, and pepper and stir to combine. Reduce the heat to medium-low and cook for about 10 minutes, until the mixture is tender and the liquid released from the mushrooms has evaporated. Remove from the heat and let cool.
Add the cannellini beans and chickpeas to a food processor and pulse into a smooth paste.
Transfer the bean paste to a large bowl and add the apple/mushroom mixture and vital wheat gluten. Mix with a spatula and then your hands until well combined.
Form the sausage mixture into a loaf, wrap in plastic wrap, and refrigerate for 2 hours.
Unwrap the chilled sausage mixture and divide into 10-12 equal pieces, depending on what size sausages you would like.
Roll a piece between your palms into a sausage shape. Place in the center of a large sheet of plastic wrap and roll the plastic over it so the sausage is completely encased. Twist the ends of the wrap and knot them together tightly. Repeat for each sausage.
Bring a large pot of water to a simmer. Plunge the wrapped sausages in the water and simmer for 45-50 minutes, until the sausages are firm.
Remove from the water and let cool for about 5 minutes, then unwrap.
Heat the remaining tablespoon of olive oil in a large skillet over medium-low heat. Fry the sausages for 1-2 minutes on each side, until golden brown.
Serve immediately or keep wrapped in the refrigerator for up to 4 days.