Place eggplant and bell pepper on a grill rack coated with cooking spray; grill 4 minutes on each side or until tender. Place bell pepper wedges in a zip-top plastic bag; seal. Let stand 15 minutes. Peel bell pepper wedges. Reserve 2 bell pepper wedges and 2 eggplant slices for Sunday's brunch. Coarsely chop remaining bell pepper and remaining eggplant. Sprinkle with 1/4 teaspoon black pepper.
Place bread slices on grill rack; grill 2 minutes on each side or until golden brown.
Place remaining 1/4 teaspoon black pepper, vinegar, oil, mustard, and salt in a large bowl; stir well with a whisk. Add eggplant, bell pepper, arugula, tomatoes, and spinach; toss gently to combine. Arrange about 2 1/2 cups salad on each of 4 plates; top each serving with 1 goat cheese slice and 1 tablespoon Sweet Chipotle Snack Mix. Serve each salad with 1 toast slice.