Grapefruit, Avocado and Fennel Salad

Ingredients:

• 2 Tbs. Champagne vinegar
• 1 1/2 tsp. finely grated grapefruit zest
• 2 Tbs. fresh grapefruit juice
• 1 Tbs. finely chopped shallot
• 2 tsp. sugar
• 1 tsp. Dijon mustard
• 1/4 cup (2 fl. oz./60 ml) walnut oil or grapeseed oil
• Kosher salt and freshly ground pepper, to taste
• 10 oz. (315 g) mâche
• 1 small fennel bulb, trimmed, cored and very thinly sliced
• 2 ruby red grapefruits, peeled and segmented
• 1 avocado, pitted, peeled and sliced