Find and replace with sed in directory and sub directories
Solution 1:
Your find should look like that to avoid sending directory names to sed:
find ./ -type f -exec sed -i -e 's/apple/orange/g' {} \;
Solution 2:
For larger s&r tasks it's better and faster to use grep and xargs, so, for example;
grep -rl 'apples' /dir_to_search_under | xargs sed -i 's/apples/oranges/g'