Combine shallots, parsley, chillies, oregano, chives, vinegar, olive oil, Tabasco, and lemon juice in a bowl.
Preheat the grill to a medium-high setting.
Fry the poussins and lemon halves in a hot ovenproof griddle pan for 2-3 minutes per side until golden-brown.
Grill the poussins for 8-10 minutes until cooked through and squeeze the roasted lemons over them.
Mix celery, walnuts, stilton, parsley, and celery leaves in a separate bowl for the salad.
Whisk together crème fraîche, honey, vinegar, and mayonnaise until the dressing is smooth.
Toss the salad with enough dressing to coat the ingredients evenly.
Serve the poussin drizzled with sauce alongside the walnut salad.