Sorry, I don't understand why you tend to discard the words that I think that are fittest.
Gaze seems a good choice to me.
According to the D.R.A.E
mirada
f. Acción y efecto de mirar. [Action related to the verb to look at]
f. Vistazo, ojeada.
f. Modo de mirar, expresión de los ojos. [How you look at something or someone]
There's nothing explicitly romantic in the definition.
According to vocabulary.com
When someone lays eyes on you and keeps looking, it is a gaze or a stare
Gaze is both a verb and a noun. When people daydream, they often gaze
off into the distance without focusing on anything. Another type of
gaze, though, is to look very intently at something, as when you gaze
at the sky making pictures out of clouds
And according to the Cambridge Dictionary
gaze [verb]
to look at something or someone for a long time, especially in surprise or admiration, or because you are thinking about something else.
As I understand it, gaze as noun represents the action of the verb to gaze.
So
Cómo olvidar tu mirada
is usually understood in a poetic or romantic sense as
Cómo olvidar cómo me mirabas intensamente con los ojos llenos de amor
Which we can translate to English as
How could I forget your gaze
meaning
How could I forget how you gaze at me so intensily and full of love
Notice that both suggested explanations, in Spanish and in English, are not explicitly set in the original sentence. The author leaves to the audience freedom to imagine what he really meant just with tu mirada / your gaze, because it can also mean in both languages that the speaker liked how the eyes of her loved one looked when she was daydreaming.
Your eyes or the look in your eyes does not reflect the original phrase [explicit] but your interpretation [implicit]. It's not a translation, it's an explanation.
