Step 1 Preheat oven to 200°C. Line a large baking tray with baking paper. Arrange sweet potato, in a single layer, on prepared tray and spray with olive oil. Bake potato for 35 minutes, or until golden and tender.
Step 2 Meanwhile, slice each chicken breast, horizontally, into 2 fillets. Spray a large frying pan with a light coating of olive oil; set over medium–high heat. Cook chicken, turning, for 7 minutes, or until browned and cooked through. Transfer chicken to a plate, cover to keep warm and set aside.
Step 3 Put mayonnaise and sun-dried tomatoes in a food processor; blend until almost smooth. Add lemon juice and 2 tablespoons water; blend to combine.
Step 4 Put 1 slice of toast on each serving plate. Top each with tomato mayonnaise, then with cucumber, alfalfa and reserved chicken, trimming filling to fit as necessary. Repeat this layer, starting with toast and finishing with chicken. Top each sandwich with remaining toast.
Step 5 Serve club sandwiches with sweet potato wedges and mixed salad greens drizzled with extra lemon juice.