Quinoa Burgers with Lime Mayonnaise

1/2 C. chopped onion, divided
1 Tbsp. olive oil plus additional for brushing
1/2 C. Quinoa, rinsed three times
1 C. water
1 C. pinto beans, rinsed and drained
1 1/2 Tbsp. soy sauce
3/4 C. walnuts
2 cloves garlic, minced
1/2 C. packed cilantro sprigs
3/4 tsp. ground cumin
1/4 tsp cayenne
1/4 C. mayonnaise
1/4 tsp grated lime zest
1/2 tsp fresh lime juice
4 slices ciabatta bread
baby greens and tomato slices

In a small heavy saucepan, over medium heat, cook half the onions with salt to taste in oil.  Stir occasionally, until golden, about 5 minutes.  Add quinoa and water, cook, covered over low heat until water is absorbed and quinoa is soft, about 15 minutes.  Transfer to a bowl and stir in beans and soy sauce.
Move quinoa mixture to a food processor and add; walnuts, garlic, cilantro, cayenne, cumin, salt and pepper to taste, and remaining onion.  Pulse mixture until finely chopped.
Form rounded 1/2 cups of mixture into 4 (3 1/2" diameter) patties.  Chill at least 10 minutes.
While patties are chilling, stir together mayonnaise, zest, and juice.
Heat grill or the patties can be cooked in a sauté pan.  Either way brush patties with olive oil and then cook until each side is golden brown, about 4 minutes per side.  Reserve warm.  Brush ciabatta slices with olive oil and grill to golden brown. Serve burgers open faced on grilled bread with lime mayonnaise.  Top with baby greens and tomato, serve and enjoy!