Making good progress over puzzle finally -- tend to be a far from lateral thinker (3,5)
'tend to be a far from lateral thinker' is the definition.
I can't judge whether this defines the answer.
'making good progress over puzzle finally' is the wordplay.
'making good progress' becomes 'ontrack'.
'over' means one lot of letters goes inside another.
'finally' says to take the final letters.
The final letter of 'puzzle' is 'e'.
'ontrack' placed around 'e' is 'ONE-TRACK'.
(Other definitions for one-track that I've seen before include "This mind can hold only a single opinion at a time" , "This mind is limited in scope to dealing with single item" , "Obsessed by single idea" , "Obsessed with a single subject" , "No racket for inflexible mind" .)
'a far from lateral thinker' is the definition.
'making good progress over puzzle finally tend to' is the wordplay.
'making good progress' becomes 'ontrack'.
'over' means one lot of letters goes inside another.
'finally' indicates one should take the final letters.
'tend to' becomes 'mind'.
The last letter of 'puzzle' is 'e'.
'ontrack' enclosing 'e' is 'onetrack'.
'onetrack'+'mind'='ONE-TRACK MIND'
'be' is the link.
(Other definitions for one-track mind that I've seen before include "Obsession with a single objective" , "Brain preoccupied with a single subject" , "A very limited thinker?" , "Obsessive attitude to a subject" , "Very basic obsession?" .)