In a large bowl combine the arugula, red onion, bell pepper, mango and radishes. Toss to combine and set aside.
In a small bowl, combine the garlic, mustard, key lime juice, olive oil, salt, pepper and cilantro. Whisk to combine and set aside.
For the Key Lime Aioli
In a small bowl combine the mayonnaise, garlic, key lime juice, lime zest, salt, pepper. Stir until well combined.
Assemble the salad
Add dressing a few tablespoons at a time to the greens and toss until salad is lightly coated. -- You may not need all the dressing and if you have leftovers just cover and refrigerate for another salad.
Divide the salad among four plates. Top each with a hot crab cake and a dollop of the Key Lime Aioli. Serve.