Preheat the oven to 375 F.
Clean at least 12 large mushrooms and remove the stems. Leave the caps aside to be stuffed. Chop the stems for part of the stuffing. Dice 1/2 an onion.
In olive oil, sauté the chopped stems, chopped pecans, breadcrumbs and a minced clove of garlic. Now add a teaspoon of lemon juice and salt and pepper to taste. Add a little more olive oil if the mixture is too dry.
Now spoon the stuffing into the caps and place them in a nonstick, oven-proof pan. Bake for about 20 minutes. Garnish with minced chives and red bell pepper.