In a large bowl, stir cooled quinoa, watermelon, bell pepper, cucumber, red onion, mango, pineapple, and chopped cilantro leaves together
Whisk together pineapple juice, lime juice, and garlic together in a small bowl; drizzle in olive oil oil, whisking constantly. Pour dressing over quinoa mixture; toss gently to combine. Place salad in a serving bowl; garnish with lime slices, jalapeno slices, and reserved cilantro leaves.