Preheat oven to 375 F°
Cut your pumpkin in half and spoon out the seeds
Cut one half into chunks
Prepare a baking dish with parchment paper
Arrange pumpkin chunks on dish
Roast for 30 minutes until soft
Place pumpkin in blender
Mix until smooth and set aside
Thinly slice onion
In a large skillet melt butter over medium-low heat
Add the onions and cook covered for 10 to 15 minutes, until the onions are tender
Uncover the skillet and cook and stir over medium-high heat for 3 to 5 minutes more or until onions are golden
Spread your bottom bread with the pumpkin spread
Add onions and walnuts
Add some greens and top with top bread