Guthix using it during your training
The Tchbqaertkchm (Commonly 'abbreviated' as the Green Kamehameha) is a regular Kamehameha with added artificial green food dye. Guthix taught it to you before you learned his gaze. When he asked you to repeat its name, you copy & pasted it.
Trivia[]
-It is one of the elements of the White Kamehameha.
-Despite the White Kamehameha being more powerful, you use this variation because it is green, and green is a traditional Guthix symbol.