A French classic from Provence, this version takes its inspiration from Ontario asparagus, greenhouse tomatoes and mushrooms. It makes a simple but sophisticated main course for dining al fresco.
Dressing: In small bowl, whisk together oil, vinegar, water, garlic, tarragon, mustard, capers, salt and pepper; set aside.
In large pot of lightly salted boiling water, cook asparagus until tender-crisp, 3 to 5 minutes. Drain and rinse under cold water; drain well. On 2 dinner plates, arrange in groups, asparagus, potatoes, mushrooms, tuna, eggs, tomato and olives; drizzle with dressing.