Place livers, mushrooms and eggs in a food processor and blend until thick and creamy. Melt butter in a skillet and sauté the onion over a medium-high heat for 5 minutes, then add the puréed liver and continue to stir for a further 5 minutes. Add the garlic, lemon juice, salt and peppers and stir well, then remove from heat and allow to cool. Remove the mixture to a cleaned processor and blend until smooth. Line a mold with plastic wrap and fill with the paté mixture, then garnish with finely chopped pecans. Refrigerate for at least 6 hours before serving with garlic toast or crackers.