THE SOLUTION:
Oscar threw a gutter ball on his first toss, then got the spare by knocking all 10 pins down with his second throw.
From then on, he scored 9 on the first ball and then picked up the spare with his second, for each of the remaining frames.
Because a spare scorex 10 plus the value of the next ball thrown, Oscar scored 19 pins in each of the ten frames for a total of 190… even with the gutter ball on his first throw.