Cook bacon in a skillet over medium heat until crisp, turning occasionally, about 7 minutes. Drain on paper towels and coarsely crumble.
Toss spinach, onion, water chestnuts, sprouts and mushrooms in a large bowl. Toss with dressing and divide among 6 plates. Sprinkle egg and bacon on top. Serve immediately.
Tip: To hard-cook eggs: Place eggs in a single layer in a saucepan; cover with water. Bring to a simmer over medium-high heat. Reduce heat to low and cook at the barest simmer for 10 minutes. Remove from heat, pour out hot water and run a constant stream of cold water over the eggs until completely cooled.