Could you prepare ahead? Would you recommend putting these sandwiches together in the morning for a picnic midday?

Thanks!!

Agree with Gammy about blackened avocado. Also the bread and greens will get mushy.
But if you want this to go, pack it in 3 parts:
• bread or roll;
• ripe avocado whole/intact;
• salad with all except avocado.
When ready for lunch, cut roll in half, cut avocado, assemble sandwich, enjoy.

I would be hesitant. I think the smashed avocado would quickly turn an unappetizing brown.