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.