In a medium bowl, toss to combine 'Group 1' tomatoes, onions, poblanos, bell peppers, and cucumbers with kosher salt. Cover and keep at room temperature for a minimum of 3 hours and up to 6 hours, to allow the vegetables to macerate in the salt.
Spread bread cubes out on a sheet pan and toast at 350°F for 10 minutes, until lightly golden. Let cool slightly.
Combine all 'Group 2' diced vegetables in a medium bowl; set aside.
In another small bowl, combine olive oil and vinegar. Add toasted bread, coat well, and let soak for 10 minutes.
Pour the vinegar-oil mixture (with soaked bread) over the macerated 'Group 1' vegetables. Add garlic and cayenne. Use a blender to puree until smooth.
Strain the puree through a fine-mesh strainer or China cap into the bowl, using a ladle to work the liquid through. Discard pulp that is left behind. Fold in the 'Group 2' small diced vegetables into the soup and mix well to combine. Store in refrigerator until chilled. Can be made the night before serving.
When ready to serve, stir gazpacho to remix and ladle into chilled soup bowls. Drizzle olive oil on top and garnish with croutons for texture.