In a small bowl, combine the vinegar and mustard, and whisk until well blended. Add the sugar, garlic, and salt and pepper; stir well and set aside.
In a large salad bowl, combine the spinach, avocado, and onion; set aside.
In a large skillet, fry the bacon over moderate heat until crisp. Drain on paper towels, and crumble coarsely. Pour off all but about 2 tablespoons grease from skillet, add the oil plus the vinegar-mustard mixture, and stir until dressing is hot. Pour dressing over spinach mixture and toss well. Add the bacon and eggs, toss well again, and taste for seasoning. Serve salad immediately.