Method 1

file "bar"
file "baz"

log "foo" do
  only_if do
    resources("file[bar]").updated ||
      resources("file[baz]").updated
  end
end

Method 2

node.default["whatever_needs_restart"] = false

file "bar" do
  notifies :run, "ruby_block[whatever_needs_restart]", :immediately
end


file "baz" do
  notifies :run, "ruby_block[whatever_needs_restart]", :immediately
end

ruby_block "whatever_needs_restart" do
  block do
    node.default["whatever_needs_restart"] = true
  end
  action :nothing
end

log "restart something" do
  only_if do
    node.default["whatever_needs_restart"]
  end
end