Arrange the baguette slices on a baking sheet. Brush each slice with a little olive oil. Toast in the preheated oven for about 5-7 minutes or until golden brown and crispy. Remove from the oven and set aside.
In a large skillet over medium heat, add the remaining olive oil. Once hot, add the minced garlic and sauté for about 1 minute until fragrant, being careful not to let it burn.
Add the shrimp to the skillet. Sprinkle with salt, pepper, and red pepper flakes if using. Cook for about 3-4 minutes, stirring occasionally, until the shrimp turn pink and are cooked through. Remove from heat.
In a small bowl, mix the mashed avocado with lemon juice, adding salt and pepper to taste.
Assemble the crostini by spreading a generous layer of avocado on each toasted baguette slice, then top with a few garlic shrimp.
Garnish with freshly chopped cilantro or parsley.
Serve immediately while the crostini is warm and enjoy!