Scoop flesh from avocado into a blender pitcher; add cucumber, green onion, cilantro, garlic, cumin, and salt. Pulse until blended.

With processor running, slowly stream coconut milk into the mixture; add the lime juice and continue to blend until smooth. Alternately, put the ingredients into a deep bowl or pot and blend with an immersion blender until smooth.

Ladle into bowls and garnish with pepitas and additional cilantro to serve.