Whisk together the serrano pepper, lime juice, rice vinegar, cilantro, salt, and pepper in a large bowl. Slowly drizzle in the olive oil while continually whisking. Add the pineapple and jicama; toss to coat. Allow to sit 30 minutes to 1 hour. Place the spring mix in a large salad bowl; scatter the avocado over the lettuce; top with the marinated pineapple and jicama, drizzling the remaining vinaigrette over the salad. Serve NOW!