Bring a medium pot of salted water to a boil and poach the shrimp for 2 to 3 minutes until opaque and pink.
Drain the shrimp and immediately submerge them in an ice water bath for 2 minutes to stop the cooking process.
In a small mixing bowl, whisk together the olive oil, lime juice, Dijon mustard, salt, and pepper until emulsified.
In a large bowl, combine the chilled shrimp, cubed avocado, diced cucumber, and minced red onion.
Pour the dressing over the ingredients and toss gently to ensure the avocado remains intact.
Arrange the baby spinach on two plates and top with the shrimp and avocado mixture.
Garnish with chopped cilantro and serve immediately.