Hello! I just published my project for this challenge. Shame that I spent a low amount of
time on the actual explosions, but I aimed to develop the game fully on ECS (with tiny-ecs)
If you curious about how it works I written some details on the Github page. Welcome to learn how it can be done in Defold 
Github: GitHub - Insality/shooting_circles: Defold ECS game example
Play here: Shooting Circles 0.0.1