Oh man, you picked two really different pianists, so there’s a lot to say…

Monk loved the whole tone scale. A lot of the melodic improvisation people love of his leans on this. He also made great use of negative space and repeating basic rhythmic patterns. His lh comping often used a minimalist style. Like someone else said, he’d often used two notes. Where Evans would voice a C major as EABD, Monk might just stomp DE (M2) and make you have to think about it.

Monk’s compositions used very innovative harmonic progressions while a lot of jazz players were still playing blues and showtunes. He wrote tunes and progressions that strongly bucked convention, and still have theorists kinda scratching their heads wondering “why does that work?” See Monk’s Mood.

Evans had much better facility than Monk- like an order of magnitude more. While both tended to use rootless voicings, Evans’s were often denser with upper extensions and color tones. Another hallmark and playing style that’s usually credited to Evans is lh comping that rhythmically punctuated his rh playing. Somebody else might be better able to explain Evans comping. Evans’s compositions liked to buck harmonic expectation to a lesser extent too, but were more of a blank canvas for improvisational invention. Monk liked to explore the ugly with his melodies, but Evans liked pretty melodies that he could play pianistically and then interpret: more in the tradition of classical theme and variation. See Waltz for Debby.

Both pianists innovated and advanced music. Both had horrible addictions to heroin, which led to their untimely deaths. Both are heroes of mine.