1. To make dressing, whisk together first 3 ingredients (through sugar) in a bowl. Add oil in a thin stream, whisking constantly. Season with salt and pepper; set aside.
2. Peel and chop lychees. Gently separate mushrooms from one another.
3. For each serving, toss 1 cup mâche with some cherry tomatoes, mushrooms, lemon cucumber, and English cucumber with 1 tablespoon dressing in a bowl. Top with 1 teaspoon chopped lychees and a dash of sea salt. (Add more lychees if you'd like a stronger floral flavor.)
*Note: If you can't find lemon cucumbers, use 8 red radishes.